Fuel cells and electrolysers usually comprise a number of stacks, which are added in combination with a proton exchange membrane (PEM), in order to obtain separated cells for the electrochemical reactions in either the fuel cell or electrolyser. Such stacks are generally known in the art. They usually have at least 3 layers, engaging each other closely.
A first layer is a water- and gas-proof layer, hereafter referred to as “collector layer”, and also referred to in the art as “bipolar plate”. This collector layer avoids gas or water leakage from one cell to an other, and guides electrons (e−) to or from the cell. Therefore it is generally known to use a conductive plate, usually a graphite plate.
A second layer, engaging closely one side of the collector layer, is used to distribute the gasses, used or provided by the electrochemical reaction in the fuel cell or electrolyser at the proton exchange membrane (PEM), over the whole surface of the fuel cell or electrolyser. This layer is hereafter referred to as “distribution layer”.
A third layer, engaging closely the other side of the collector layer, is a layer, used to provide the contact between diffusion layer and PEM. At this so-called contact layer or “electrode layer”, the electrochemical reaction takes place, due to the presence of catalytic elements, either on the contact layer or the PEM itself. Gasses, being provided via the diffusion layer to this contact layer, are to be retained sufficiently to enable the electrochemical reaction to take place.
The contact layer, and possibly also the diffusion layer, may be made hydrophobic (e.g. by impregnation or presence of hydrophobic elements such as Teflon®) or hydrophilic.
Depending on the place of the stack in the fuel cell or the electrolyser, a electrochemical reaction takes place in which e−, protons (H+) and a gas are consumed or provided near a PEM.
The H+ are provided or evacuated via the PEM to the electrochemical reaction. Therefore, the contact between contact layer and PEM is to be as perfect as possible, since the electrochemical reaction takes place at the catalytic layer, which is close to the surface of the PEM.
The e− are provided or evacuated via the stack of collector layer, diffusion layer and contact layer. Therefore, all layers engaged are to be electro-conductive, and the resistance over the stack, and especially the contact resistance at the contacts of the several layers is to be as low as possible.
The diffusion layer is to spread the gas flow as much as possible over the whole surface of the contact layer, in order to use the present catalytic elements as complete as possible, providing e− and H+ over the whole surface of the PEM.
An example of a stack is described in WO0069003 and EP0141241.
Further it is known that the mechanical connection of a sintered connection between a metal plate or foil and a metal mesh or expanded metal sheet or sheet of foamed metal, may be relatively weak. This weakness, resulting in a release between both materials, may lead to higher electrical contact resistance between both layers, since this resistance is determined by a strong and firm contact of both surfaces.